Understanding through Discussion


Welcome! You are not logged in. [ Login ]
EvC Forum active members: 79 (8908 total)
Current session began: 
Page Loaded: 05-26-2019 10:12 AM
21 online now:
JonF, Thugpreacha (AdminPhat) (2 members, 19 visitors)
Chatting now:  Chat room empty
Newest Member: WeloTemo
Post Volume:
Total: 852,050 Year: 7,086/19,786 Month: 1,627/1,581 Week: 6/443 Day: 6/34 Hour: 0/3


Thread  Details

Email This Thread
Newer Topic | Older Topic
  
Prev1
2
3456Next
Author Topic:   What Creates Gravity?
Dr Adequate
Member
Posts: 16094
Joined: 07-20-2006
Member Rating: 5.5


Message 16 of 84 (390686)
03-21-2007 2:54 PM
Reply to: Message 15 by zcoder
03-21-2007 2:41 PM


Well, when you drop something, the force of gravity accelerates it downwards: this has the effect of turning its potential energy into knetic energy (which is dispersed as heat (also energy) and sound (more energy) when the object hits the ground).

The gravitational force doesn't make energy: energy is conserved. The action of gravity turns one sort of energy into another.

I hope this answers your question: I wasn't quite sure what you were asking.


This message is a reply to:
 Message 15 by zcoder, posted 03-21-2007 2:41 PM zcoder has responded

Replies to this message:
 Message 17 by zcoder, posted 03-21-2007 3:06 PM Dr Adequate has not yet responded

  
zcoder
Member (Idle past 4350 days)
Posts: 66
Joined: 03-19-2007


Message 17 of 84 (390688)
03-21-2007 3:06 PM
Reply to: Message 16 by Dr Adequate
03-21-2007 2:54 PM


yeah, I think that explains it.
anyways I was reading a article about dark matter expelling energy
though out the universe and is lost. something like that, anyway I took it
that space is someday going to cool down and then, well no one knows
what will happen then.

But the article was not very clear as to how the energy in the universe was
being spent.

Zcoder....


This message is a reply to:
 Message 16 by Dr Adequate, posted 03-21-2007 2:54 PM Dr Adequate has not yet responded

    
fallacycop
Member (Idle past 3662 days)
Posts: 692
From: Fortaleza-CE Brazil
Joined: 02-18-2006


Message 18 of 84 (390713)
03-21-2007 4:31 PM
Reply to: Message 15 by zcoder
03-21-2007 2:41 PM


Umm, I am confused.

Most sensible thing you've said so far
This message is a reply to:
 Message 15 by zcoder, posted 03-21-2007 2:41 PM zcoder has responded

Replies to this message:
 Message 19 by zcoder, posted 03-21-2007 4:35 PM fallacycop has not yet responded

  
zcoder
Member (Idle past 4350 days)
Posts: 66
Joined: 03-19-2007


Message 19 of 84 (390715)
03-21-2007 4:35 PM
Reply to: Message 18 by fallacycop
03-21-2007 4:31 PM


is it a felony to be confused?
Umm double confused

Zcoder....


This message is a reply to:
 Message 18 by fallacycop, posted 03-21-2007 4:31 PM fallacycop has not yet responded

Replies to this message:
 Message 22 by RAZD, posted 06-16-2007 8:24 AM zcoder has not yet responded

    
CosmicChimp
Member
Posts: 306
From: Muenchen Bayern Deutschland
Joined: 06-15-2007


Message 20 of 84 (405965)
06-15-2007 5:36 PM
Reply to: Message 1 by zcoder
03-19-2007 11:17 AM


You mention that space is expanding. The universe is expanding. Do you mean to say that the universe is expanding away from the ball?
This message is a reply to:
 Message 1 by zcoder, posted 03-19-2007 11:17 AM zcoder has not yet responded

Replies to this message:
 Message 21 by Taz, posted 06-15-2007 9:53 PM CosmicChimp has acknowledged this reply

  
Taz
Member (Idle past 1433 days)
Posts: 5069
From: Zerus
Joined: 07-18-2006


Message 21 of 84 (405997)
06-15-2007 9:53 PM
Reply to: Message 20 by CosmicChimp
06-15-2007 5:36 PM


What ball?



We are BOG. Resistance is voltage over current.

Disclaimer:

Occasionally, owing to the deficiency of the English language, I have used he/him/his meaning he or she/him or her/his or her in order to avoid awkwardness of style.

He, him, and his are not intended as exclusively masculine pronouns. They may refer to either sex or to both sexes!


This message is a reply to:
 Message 20 by CosmicChimp, posted 06-15-2007 5:36 PM CosmicChimp has acknowledged this reply

  
RAZD
Member
Posts: 19845
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 5.7


(2)
Message 22 of 84 (406024)
06-16-2007 8:24 AM
Reply to: Message 19 by zcoder
03-21-2007 4:35 PM


is it a felony to be confused?

No but it is a misdemeanor to stay confused. Get thee to a nunnery library and read up on gravity, special relativiey, general relativity, brane theory, string theory, and wherever these lead. Start with readable versions first: I'm sure Cavediver can recommend some popular books that give a good overview.

One I have read and enjoyed was The Dancing Wu Li Masters: An Overview of the New Physics by Gary Zukav - Bantam ; Reissue edition (September 1, 1984).

There is also The Tao of Physics by Fritjof Capra

and
The Fabric of the Cosmos: Space, Time, and the Texture of Reality and The Elegant Universe, by Brian Greene

It will lead to more questions than answers, but it also leads out of your current state of confusion. Questions lead to more refined search for answers.

Enjoy.


Join the effort to unravel AIDS/HIV, unfold Proteomes, fight Cancer,
compare Fiocruz Genome and fight Muscular Dystrophy with Team EvC! (click)


we are limited in our ability to understand
by our ability to understand
RebelAAmericanOZen[Deist
... to learn ... to think ... to live ... to laugh ...
to share.

This message is a reply to:
 Message 19 by zcoder, posted 03-21-2007 4:35 PM zcoder has not yet responded

Replies to this message:
 Message 23 by anglagard, posted 06-16-2007 5:06 PM RAZD has not yet responded

  
anglagard
Member
Posts: 2185
From: Socorro, New Mexico USA
Joined: 03-18-2006


Message 23 of 84 (406065)
06-16-2007 5:06 PM
Reply to: Message 22 by RAZD
06-16-2007 8:24 AM


Pop Physics Indeed!
Zukav and Capra, good Lord!

The next time any Lophophora williamsii goes missing around here, I say check the nearest physics department.


This message is a reply to:
 Message 22 by RAZD, posted 06-16-2007 8:24 AM RAZD has not yet responded

    
Rahvin
Member (Idle past 1328 days)
Posts: 3964
Joined: 07-01-2005


Message 24 of 84 (406072)
06-16-2007 6:39 PM
Reply to: Message 15 by zcoder
03-21-2007 2:41 PM


yeah, thats right, but if that force has already pushed things down
to the surface of an object, then was it not used as energy?
expelled as work?

No. The work was raising the object in the first place. When the object falls, it is simply returning to a lower level of potential energy, increasing entropy. Gravity cannot be "used up," any more than magnetism or the Strong/Weak atomic forces. It's a basic property or matter - as has been said, it's existence is part of matter's definition. And if you recall the rest of the Law of Thermodynamics, you'll rememeber that matter cannot be created or destroyed.


Every time a fundy breaks the laws of thermodynamics, Schroedinger probably kills his cat.
This message is a reply to:
 Message 15 by zcoder, posted 03-21-2007 2:41 PM zcoder has not yet responded

Replies to this message:
 Message 46 by Buzsaw, posted 07-13-2008 1:02 PM Rahvin has not yet responded

  
dkv
Member (Idle past 3874 days)
Posts: 38
Joined: 09-15-2007


Message 25 of 84 (474905)
07-12-2008 3:14 AM


Gravity is sometimes understood as geometry of space time.
General theory of relativity says that the space time wraps due to the presence of mass. There is no force just a geometry.
However I have my doubts.
General theory of relativity is based on the principle of equivalence.
Which in my opinion is fundamentally flawed.

"The principle of equivalence: There is no experiment observers can perform to distinguish whether an acceleration arises because of a gravitational force or because their reference frame is accelerating

– Douglas C. Giancoli Physics for Scientists and Engineers with Modern Physics, p. 155"

However note that GMm/r^2=ma ; a= GM/r^2 (acceleration is independent of mass but not independent of the distance from the source of gravity)
therefore as the distance between gravitational center and the center of frame decreases the acceleration increases ... this can be used to distinguish between gravitational and non-gravitational frames.
Experiment :A body falls freely towards Earth because the force is inversely propotional to distance between earth and object ,as it falls it will experience an increase in acceleration due decrease in the distance(g=9.8m/s^2 is only an approximation because change in R is small). Therefore if a sufficiently sensitive instrument is available then it should be possible to detect the increase in acceleration thus violating the equivalence principle.
Moreover spatially distributed point masses experiences different accelerations.
It is in principle possible to differentiate between a accelerating frame and gravitationally accelerating frame.


Replies to this message:
 Message 27 by cavediver, posted 07-12-2008 5:53 AM dkv has responded

    
Syamsu 
Suspended Member (Idle past 3731 days)
Posts: 1914
From: amsterdam
Joined: 05-19-2002


Message 26 of 84 (474909)
07-12-2008 5:45 AM
Reply to: Message 1 by zcoder
03-19-2007 11:17 AM


"The Newton law of gravitation is based on an instantaneous propagation of gravity, and the Newtonian equations for the solar system, for example, work rather well, except for the anomalous perihelion of the planet Mercury. General relativity explains this aberration. In taking into account the retarded gravitational potential in the Newtonian equation, the equation of general relativity is obtained in introducing anticipative propagation of the gravitational field. "

http://www.mindspring.com/~cerebroscopic/Dubois.html

So what this means basically, is that general relativity is derived from Newtonian gravity, and that in an information view of things, objects are computing their next state with the equations of gravity itself. So to say, the objects consist of the equations of gravity, and the particular values they have for the variables, past, present and future. The objects are information computing units.

Now what is the origin of the particular values of the variables? Note how anticipation is a time principle, it is instantaneous. The origin of the values come from a decision for every step in time, which freedom still obeys the conservation of properties.


This message is a reply to:
 Message 1 by zcoder, posted 03-19-2007 11:17 AM zcoder has not yet responded

Replies to this message:
 Message 28 by Dr Adequate, posted 07-12-2008 6:27 AM Syamsu has not yet responded

    
cavediver
Member (Idle past 1785 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 27 of 84 (474910)
07-12-2008 5:53 AM
Reply to: Message 25 by dkv
07-12-2008 3:14 AM


General theory of relativity is based on the principle of equivalence.

No - the principle of equivalence helped lead Einstein to the General Theory, but the EP is a *prediction* of GR as we formulate it.

Which in my opinion is fundamentally flawed.

First check - if you think your simple hunch is going to overturn 100 years of physics and the thinking of the greatest physicists of recent times such as Einstein, Hawking, Feynman, Dirac, Pauli, Cavediver (I wish) - then you should probably doubt your hunch first. Trust me - been there, done that.

"The principle of equivalence: There is no experiment observers can perform to distinguish whether an acceleration arises because of a gravitational force or because their reference frame is accelerating

Unfortuanetly, either you or Prof Giancoli is missing an exteremly important word - LOCAL. This should read:

"The principle of equivalence: There is no LOCAL experiment observers can perform to distinguish whether an acceleration arises because of a gravitational force or because their reference frame is accelerating"

And sadly the rest of your argument now falls apart. Of course we can distinguish the acceleration if we can look sufficiently far around us to notice the tidal effects of the gravitational field. But this is irrelevant for the equivalence principle.

A body falls freely towards Earth because the force is inversely propotional to distance between earth and object ,as it falls it will experience an increase in acceleration due decrease in the distance(g=9.8m/s^2 is only an approximation because change in R is small). Therefore if a sufficiently sensitive instrument is available then it should be possible to detect the increase in acceleration thus violating the equivalence principle.

No - you cannot detect any acceleration if you are freely falling! What you could detect with your sensitive instrument, is the difference between what is happening at the top of your frame and what is happening at the bottom of the frame. This is where the differential gravitational field will be noticed. A partcile at the top of your frame will be moving away from a particle at the bottom of your frame. Two partciles on either side of your frame will actually be moving towards each other. But again, these ar not LOCAL experiments as you are comparing partciles at different points. All you are doing is discovering that your lcoal space-time curvature is changing as you move through space-time - nothing unusual there...

That all said - it is quite possible that the equivalence principle is not infallible, but it will not be because of a failure of GR, but because of corrections to GR resulting from quantum gravity.


This message is a reply to:
 Message 25 by dkv, posted 07-12-2008 3:14 AM dkv has responded

Replies to this message:
 Message 29 by dkv, posted 07-12-2008 8:59 AM cavediver has responded

  
Dr Adequate
Member
Posts: 16094
Joined: 07-20-2006
Member Rating: 5.5


Message 28 of 84 (474911)
07-12-2008 6:27 AM
Reply to: Message 26 by Syamsu
07-12-2008 5:45 AM


That was ... very odd.
This message is a reply to:
 Message 26 by Syamsu, posted 07-12-2008 5:45 AM Syamsu has not yet responded

  
dkv
Member (Idle past 3874 days)
Posts: 38
Joined: 09-15-2007


Message 29 of 84 (474922)
07-12-2008 8:59 AM
Reply to: Message 27 by cavediver
07-12-2008 5:53 AM


EQuivalence Principle is a principle because it is one of the basic postulates of General relativity. Experiments have supported it.(no amount of experiment can prove a theory... one single experiment can disprove a theory...observations can only "support" a theory)
There is Weak Equivalence principle and there is strong equivalence priciple using which a theory was proposed and the predictions were made.
Therefore IMO it is wrong to say that EP is a prediction of the theory.
Why do we suspend our skeptisim when discussing Einstein's theory?
Was einstein right ? Had he had the last say on nature of universe ?
No. Einstein's GR totally fails are microscopic levels...


No - you cannot detect any acceleration if you are freely falling! What you could detect with your sensitive instrument, is the difference between what is happening at the top of your frame and what is happening at the bottom of the frame. This is where the differential gravitational field will be noticed. A partcile at the top of your frame will be moving away from a particle at the bottom of your frame. Two partciles on either side of your frame will actually be moving towards each other. But again, these ar not LOCAL experiments as you are comparing partciles at different points. All you are doing is discovering that your lcoal space-time curvature is changing as you move through space-time - nothing unusual there...

That all said - it is quite possible that the equivalence principle is not infallible, but it will not be because of a failure of GR, but because of corrections to GR resulting from quantum gravity.

Local Frame from my point of view is made up of finite volume.. Which when subjected to a gravitational force experiences a non-uniform stress.
i.e the acceleration at the top and bottom of the frame is not the same.
Gravitation is Forcibly assumed UNIFORM in this local metric.
Which is not the case in reality.


"The principle of equivalence: There is no LOCAL experiment observers can perform to distinguish whether an acceleration arises because of a gravitational force or because their reference frame is accelerating"

Observers can not perform ANY experiment in the LOCAL frame as defined by GR.
Let us ask is it really a Local reference frame?
All experiments return a ratio between observed and the standard.
In a local frame we must be able to keep a standard measurement.
In the LOCAL defined by GR can we keep a standard to measure?
for example in order to measure time we need a atomic clock.. is it possible to keep a atomic clock in such a infinitely small metric.
It is obvious that we can not keep local standard measurements to define the local reference frame.
(rocket or train compartment is valid a reference frame because the local standards can be kept there.. note that everything is relative therefore it should always be possible to define the local measurements.)

Local frame as defined by GR can not be defined at all because in such case the local measurements can not be made.

Therefore IMO the EP is conceptually incorrect and therefore the GR is also incorrect.


This message is a reply to:
 Message 27 by cavediver, posted 07-12-2008 5:53 AM cavediver has responded

Replies to this message:
 Message 30 by Dr Adequate, posted 07-12-2008 10:38 AM dkv has not yet responded
 Message 32 by cavediver, posted 07-12-2008 12:46 PM dkv has not yet responded

    
Dr Adequate
Member
Posts: 16094
Joined: 07-20-2006
Member Rating: 5.5


Message 30 of 84 (474925)
07-12-2008 10:38 AM
Reply to: Message 29 by dkv
07-12-2008 8:59 AM


Therefore IMO the EP is conceptually incorrect and therefore the GR is also incorrect.

You should write to physicists about that. Make sure that you write your letters in purple ink, to let them know you're serious.


This message is a reply to:
 Message 29 by dkv, posted 07-12-2008 8:59 AM dkv has not yet responded

  
Prev1
2
3456Next
Newer Topic | Older Topic
Jump to:


Copyright 2001-2018 by EvC Forum, All Rights Reserved

™ Version 4.0 Beta
Innovative software from Qwixotic © 2019